Reducing washers as bonding method (sanity check)

[jaggedben]

Here is what happened to us yesterday....

We installed a PV system (string inverter), and like we always do we used bonding bushings on all connectors and bonded all metal enclosures. This included a DC disconnect with an eccentric knockout and a PV meter socket with a concentric knockout. If it matters, the DC side is over 250V to ground and the AC side isn't.)

The inspector said that we need a 'positive bond' around the eccentric and concentric knockouts, and that the way we are supposed to do that is to sand off the paint around the knockouts and install reducing washers on the connectors. I'm not entirely sure, but I guess he is saying that we are not allowed to use the correct size knockout for our raceway but must use a larger one.

Is the inspector making any sense at all?

 

[Smart $]

Most emphatically... NO.

 

[iwire]

Most emphatically... NO.

I can't completely agree.

While the inspectors suggestion is not the only way, it is one allowable method when the concentric KOs are not listed for grounding.

Strange as it sounds reducing washers are listed for grounding.

 

[infinity]

Is sanding off the paint around KO's ever required for the connection of a raceway?

 

[iwire]

Is sanding off the paint around KO's ever required for the connection of a raceway?

IMO it is when using fitting that are not designed to penetrate the paint such as reducing washers.

250.12 Clean Surfaces. Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.

 

[augie47]

IMO it is when using fitting that are not designed to penetrate the paint such as reducing washers.

I agree and I thought it was specifically pointed out foe reducing washers in some publication.
Another interesting fact is shown in the UL white Book under QCRV which may be the reasoning behind the inspectors call.:

GROUNDING
Metal reducing washers are considered suitable for grounding for use in
circuits over and under 250 V and where installed in accordance with
ANSI/NFPA 70, ??National Electrical Code.?? Reducing washers are intended
for use with metal enclosures having a minimum thickness of 0.053 in. for
non-service conductors only. Reducing washers may be installed in enclosures
provided with concentric or eccentric knockouts, only after all of the
concentric and eccentric rings have been removed. However, those enclosures
containing concentric and eccentric knockouts that have been certified
for bonding purposes may be used with reducing washers without all
knockouts being removed.

 

[kwired]

I can't completely agree.

While the inspectors suggestion is not the only way, it is one allowable method when the concentric KOs are not listed for grounding.

Strange as it sounds reducing washers are listed for grounding.

But OP said he used bonding bushings as well, so there wasn't really any thing left "unbonded" in his case.

 

[iwire]

But OP said he used bonding bushings as well, so there wasn't really any thing left "unbonded" in his case.

And to that I agree and why I responded as I did.

 

[Smart $]

I can't completely agree.

While the inspectors suggestion is not the only way, it is one allowable method when the concentric KOs are not listed for grounding.

Strange as it sounds reducing washers are listed for grounding.

Perhaps, but not in the context of the OP...

... we used bonding bushings on all connectors and bonded all metal enclosures. This included a DC disconnect with an eccentric knockout and a PV meter socket with a concentric knockout. If it matters, the DC side is over 250V to ground and the AC side isn't.)

Additionally, there is...

250.97 Bonding for Over 250 Volts. For circuits of over​

250 volts to ground, the electrical continuity of metal raceways​

and cables with metal sheaths that contain any conductor​

other than service conductors shall be ensured by​

one or more of the methods specified for services in​

250.92(B), except for (B)(1).

Exception omitted for brevity.​

250.92 Services.
...
(B) Method of Bonding at the Service. Bonding jumpers​

meeting the requirements of this article shall be used around​

impaired connections, such as reducing washers or oversized,​

concentric, or eccentric knockouts. Standard locknuts or bushings​

shall not be the only means for the bonding required by​

this section but shall be permitted to be installed to make a​

mechanical connection of the raceway(s).​

Electrical continuity at service equipment, service raceways,​

and service conductor enclosures shall be ensured by​

one of the following methods:​

(1) Bonding equipment to the grounded service conductor​

in a manner provided in 250.8​

(2) Connections utilizing threaded couplings or threaded​

hubs on enclosures if made up wrenchtight​

(3) Threadless couplings and connectors if made up tight​

for metal raceways and metal-clad cables​

(4) Other listed devices, such as bonding-type locknuts,​

bushings, or bushings with bonding jumpers​

 

[iwire]

Perhaps, but not in the context of the OP..

Even in the context of the OP I personally feel this response

Most emphatically... NO.

Is overstating things. To each their own.

 

[augie47]

For clarity, I agree with all in regard to no such action was necessary. I posted the info from the White Book as it was "new to me" and I felt it might be the basis for the inspector's "wrong" call.

 

[jaggedben]

Thanks for the responses. I probably should have titled the thread slightly differently.

Does anyone think, given the bonding bushings, that this redundant bonding with paint removal and reducing washers is necessary?

Also, if it's the type of lock ring with teeth that dig into and scratch the paint, do I have to do more sanding and add the reducing washers on the AC side where 250.92 doesn't apply? Could we have not even left out the bonding bushing on the AC side? The inspector was specifically concerned about the eccentric and concentric knockouts and not other cases.

BTW, this is really horrible code writing...

250.12 Clean Surfaces. Nonconductive coatings ... shall ... be connected by means of fittings designed so as to make such removal unnecessary.

Aside from the bad parallel construction, it's not clear if 'connected' means mechanically or electrically.

 

[iwire]

Does anyone think, given the bonding bushings, that this redundant bonding with paint removal and reducing washers is necessary?

With the bonding bushings already in place I do not believe any more action is required by the NEC.

 

[Smart $]

...
Aside from the bad parallel construction, it's not clear if 'connected' means mechanically or electrically.

JMO, being the Code is electrical based, I take connected to mean electrically and mechanically, secured to mean mechanically only.